1. Field of the Invention
The present invention concerns an electroconductive silicone rubber particulate which is well-suited to use as an electroconductive additive or anti-charge agent for a variety of materials including various types of rubber and organic resins.
2. Background Information
Silicone rubber particulates and their methods of manufacture are known in the art (see Laid-open Patent No. 59-68,333, which teaches the formation of silicone rubber particles by curing by heat or irradiation in a spray drier). However, electroconductive silicone rubber particulates and in particular electroconductive silicone rubber particulates well-suited to use as electroconductive additives and anti-charge agents have been unknown to date. The fact that an object molded of silicone rubber would show electrical conductivity when an electroconductive material such as carbon black had been added to and mixed into the silicone rubber composition from which the object was formed is known in the art (see Japanese Laid-open Patent No. 57-91,250, which teaches a conductive silicone rubber composition containing furnace black, with acetylene black as an optional ingredient which is foamed and cured to give an electrically conductive sponge). An electrically conductive curable liquid organopolysiloxane composition which contains a specific carbon black is taught in U.S. Pat. No. 4,273,697, issued June 16, 1981. The addition of chopped graphite fibers into an electrically conductive silicone elasomeric mixture is taught in U.S. Pat. No. 4,279,783, issued July 21, 1981. A cured unitary molded article containing conductive and insulating silicone rubber components is taught in U.S. Pat. No. 4,505,848, issued Mar. 19, 1985.
Electroconductive materials such as carbon black, when added to and mixed into a silicone rubber composition, have not always provided uniform conductivity throughout the entire silicone rubber molded product. It has also been difficult to control the level of conductivity, and particularly with regard to anti-charge and anti-electrostatic properties in semiconductive areas, it has been difficult to provide semiconductivity within the target range. The inventors of the present invention carried out extensive investigations leading to results which culminated in the present invention.